Oxidizer composition comprising nitrogen tetroxide, tetranitromethane and nitromethane



GIZER COMPGSITION COMPRISING NITRO- GEN TETROXKDE, TETRANHTRGMET ANDNHTROMETHANE John 0. Collins, Eau Claire, Win, and Stephen P. Terpko,

Winchester, Mass, assignors to Callery Chemical Company, Pittsburgh,Pa., a corporation of Pennsylvania No Drawing. Filed Dec. 23, 1960, Ser.No. 78,180

4- Claims. (Cl. 1491) This invention relates to new and useful liquidoxidizer mixtures for rocket propellant applications and in particularit relates to binary and ternary mixtures having improved properties.

The expression propellant is generally used to refer to those materialswhich release chemical reaction energy and/ or generate gases necessaryto serve as working fluid in thermodynamic expansion. Propellantcomponents are those materials which are the constituents of thepropellant and may be further classified, according to theircontribution in the propellant reaction, as fuels, oxidizers, andadditives. The latter usually serve to control or modify propellantcharacteristics and properties including burning rates, storagestability, ignition properties, and freezing and boiling points.Propellants which are self sufiicient without requiring additives are,in general, to be desired since such additives usually detract from thepropellants specific impulse although otherwise desirable for thecorrection of particular deficiencies in the propellant.

There are several liquid oxidizers now used in rocket propulsion, mostcommon of which are liquified oxygen, fuming nitric acid and hydrogenperoxide. These oxidizers have some physical and chemical propertieswhich are undesirable. Thus, an extensive search has been made to findliquid oxidizer mixtures having the best compromise of the followingproperties: high density, a liquid temperature range to include ambientconditions, low viscosity at operating temperature, stability tomechanical and thermal shock, stability during storage,non-corrosiveness, little or no toxicity, economy of production, ease ofignition and high specific impulse with common fuels. Mixtures whichmeet most of these ideal requirements have now been found and aredescribed hereinafter.

In rocket propellant considerations ambient temperature refers to thetemperature of the rocket launching site, the place of propellant usage.This may vary from the tropics to the Arctic-a possible range of fromabove 40 C. to below 40" C. Special heating or refrigerationinstallations are eliminated with liquid propellant components whichremain liquid at ambient temperature. Hydrocarbon or hydrocarbonderivative fuels, the commonly used liquid fuels, possess a liquid rangebroader than the extremes of ambient temperatures encountered. However,many of the liquid oxidizers of actual or poten tial application inrocket propulsion offer many problems in the maintenance of the liquidstate at these ambient temperatures. Liquid oxygen, for example, must berefrigerated under any condition of use.

It is an object of this invention to provide new and improved liquidoxidizer mixtures for rocket propellant applications.

Another object is to provide completely miscible liquid binary andternary oxidizer mixtures formulated from nitrogen tetroxide,tetranitromethane, and nitromethane which have a wider liquid range thannitrogen tetroxide alone and are stable against oxygen evolution.

A further object is to provide additives for liquid oxidizers forpropellant systems which do not detract from the propellants specificimpulse.

Other objects will become apparent from the specification and appendedclaims.

These new and improved liquid propellant oxidizer mixtures will be morefully described hereinafter and the novelty thereof will be particularlypointed out and distinctly claimed.

, This invention is based upon the discovery that the addition ofnitroparaffins such as nitromethane and tetra-.

nitromethane to nitrogen tetroxide will lower both the freezing pointand vapor pressure of the latter without substantially reducing thespecific impulse attainable when used with typical hydrocarbon fuels.The binary and ternary mixtures remain liquid over a wider temperaturerange than nitrogen tetroxide alone but still possess high oxidizingpower and are much more stable. It has also been discovered thatnitromethane and nitrogen tetroxide form binary and ternary mixtureswith tetranitromethane to dramatically lower the freezing point of thelatter to produce a stable highly oxidizing propellant component.

Nitrogen tetroxide itself is a good oxidizer but it has an extremelynarrow liquid range, melting at 9.3 C. and boiling at 213 C.Tetranitromethane, another good oxidizer, freezes at 13.8 C., which istoo high for usual liquid propellant applications, and boils at 125.7 C.Nitromethane melts at -28.6 C. and boils at 101.3 C. Thus, we havediscovered that these two good oxidizers, nitrogen tetroxide andtetranitromethane, can be sub stantially improved in properties byintermixing these to form binary mixtures and/ or intermixing these withnitromethane to form binary and ternary mixtures.

In an effort to improve the liquid range of nitrogen tetroxide withadditives, it was discovered that tetranitromethane and nitromethanewere compatible with nitrogen tetroxide, forming one liquid phase in allproportions without evolution of oxygen, and most significantly it wasdiscovered that a wide range of useful oxidizer compositions withvarying properties could be obtained from suitable mixes of thesesubstances.

Thus, it was discovered that the very narrow liquid range of nitrogentetroxide of only 30L6 C. could be broadened and varied by the additionof different quantities of tetranitromethane and nitromethane. As eitherof these materials are added to nitrogen tetroxide the boiling point ofthe mixture increases. For example, the binary mixture of nitrogentetroxide with tetranitromethane (mol percentage of N 0 stated) boils at30 C. with about 60 mol percent, at 40 C. with about 44 mol percent, at50 C. with about 34 mol percent, and at 60 C. with about 27 mol percent.A smaller molar quantity of tetranitromethane is required to raise theboiling point of nitrogen tetroxide a specific amount than is requiredof either nitromethane or a mixture of tetranitromethane andnitromethane. Thus, both a composition containing about 36 mol percent N0 and 64 mol percent CH NO and a composition of 36 mol percent N 0 32mol percent C(N0 and 32 mol percent CH NO boil at about 40 C. Inaddition to the compositions containing nitrogen tetroxide describedabove, we have discovered that mixtures of tetranitromethane andnitromethane are uniformly high boiling with the lowest boiling mixtureof the two being 92 C. occurring at the azeotrope containing about molpercent nitromethane.

In reducing the freezing point of nitrogen tetroxide it was found thatthe lowest temperature that could be arrived at with tetranitromethaneas the additive was 30" C. the freezing point of the eutectic containing59 mol percent of N 0,. In order to further reduce the freezing pointnitromethane must be added. For example, we have discovered that themost oxygen rich ternary mixture freezing at 40 C. contains about 53 molpercent N 0 25 mol percent C(NO and 22 mol percent CH NO while the mostoxygen rich ternary mixture freezing at 50 C. contains about 47 molpercent N 0,, 19 mol percent C(NO and 34 mol percent CH NO Patented Aug.25, 1964 3 These two ternary mixtures will boil at 33 C. and 35 C.respectively. Still lower freezing points can be obtained at or near thetwo eutectic compositions indicated below:

Whether nitrogen tetroxide or tetranitromethane is an additive to theother is not significant, since in either case the resulting mixturewill be a good oxidizer with improved properties. However, nitromethaneis considered solely as an additive although it may be present insignificant amounts. For oxygen availability it has been found desirableto limit the amount of nitromethane in any binary or ternary mixture toabout 70 mol percent and it is preferred that it be below this amount.Significantly the properties ordinarily desired may be obtained withlesser amounts of nitromethane and in some uses it is entirely absent.Additionally it is preferred, although it is not a necessity, that theamount of any constituent, when present, be at least 5 mol percent sothat it may produce a significant beneficial efiect on properties.

As described herein it is possible to obtain specific compositions whichare usable over a wide range of ambient conditions by incorporatingtogether in suitable proportions any two or three of thecompoundsnitrogen. tetroxide, tetranitromethane, and nitromethane. Ifhighly oxidative compositions are desired, nitrogen tetroxide,tetranitromethane and nitromethane are utilized in the order named. Ifhigh boiling mixtures are required, compositions containingtetranitromethane, nitromethane and/ or nitrogen tetroxide, listed inthe order of effectiveness, are formulated. If a low freezing point isdesired, mixtures containing nitromethane, nitrogen tetroxide and/ortetranitromethane, listed in the order of effectiveness, are formulated;however, as already indicated it is only possible to go below 37.5 C.with binary or ternary mixtures containing both nitrogen tetroxide andnitromethane. Thus it is seen that each compound makes its own specialcontribution to the mixture permitting a great variety of completelymiscible mixtures of oxidizers to be formulated. General all purposeoxidizer mixtures can be made on the one hand and special purposeoxidizers on the other, all

4 having superior physical properties over the individual constituentsand being stable against oxygen evolution.

Since tetranitromethane and nitrornethane contain a hydrocarbon groupwhich acts as a fuel in the propellant combustion, the greater theproportion of these materials that are present in the oxidizercomponent, the less fuel component is required for the propellant. Whenthe fuel component is a hydrocarbon there is no material overall effecton the specific impulse of the propellant resulting from theintroduction of fuel elements with the oxidizer. However, when the fuelis a higher performance fuel, it is preferred to use oxidizer mixturesof our invention having a higher oxidizing potential.

This application is a continuation-in-part application of ourapplication field July 8, 1955, Serial Number 520,917, now abandoned.

According to the provisions of the patent statutes we have explained theprinciple and mode of practicing our invention and have described whatwe now consider to be its best embodiments. However, we desire to haveit understood that, within the scope of the appended claims theinvention may be practiced otherwise than as specifically described.

I We claim:

1. A liquid oxidizer composition for use in rocket propulsion whichconsists essentially of a mixture of from about 33 to about mol percentnitrogen tetroxide, from about 5 toabout 41 mol percenttetranitromethane, and from 0 to about 56.5 mol percent nitromethane.

2. A composition according to claim 1 in which the concentration ofnitrogen tetroxide is about 33 mol percent, the concentration oftetranitromethane is about 10.5 mol percent, and the concentration ofnitromethane is about 56.5 mol percent.

3. A liquid oxidizer composition for use in rocket propulsion whichconsists essentially of about 59 mol percent nitrogen tetroxide andabout 41 mol percent tetranitromethane.

4. A liquid oxidizer composition for use in rocket propulsion whichconsists essentially of a mixture of from about 33 to about 95 molpercent nitrogen tetroxide, and from about 5 to about 41 mol percenttetranitromethane.

References Cited in the file of this patent UNITED STATES PATENTS MorrowAug. 15, 1944 Hannum Feb. 5, 1952 OTHER REFERENCES

1. A LIQUID OXIDIZER COMPOSITION FOR USE IN ROCKET PROPULSION WHICHCONSISTS ESSENTIALLY OF A MIXTURE OF FROM ABOUT 33 TO ABOUT 95 MOLPERCENT NITROGEN TETROXIDE, FROM ABOUT 5 TO ABOUT 41 MOL PERCENTTETRANITROMETHANE, AND FROM 0 TO ABOUT 56.5 MOL PERCENT NITROMETHANE.